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The hydrologic analysis indicates the magnitude of flood peaks in Fourmile Canyon and Wonderland Creek without spills from Fourmile Canyon Creek, shown on Table 3, are similar to the regulatory flood peaks. Please note the regulatory flood peak estimates of Wonderland Creek included the estimated spill discharge of Fourmile Canyon Creek. The analysis indicates storage within Wonderland Lake above the emergency spillway reduces flood peaks along Wonderland Creek; during the 100-year event, about 22 ac-ft of storage reduces the incoming discharge of approximately 570 cfs to approximately 250 cfs at the outfall of the Lake. Table 3. Update of Flood Peak Discharge (cfs), No Spill from Fourmile Canyon Creek to Wonderland Creek ourml e anyon ree Location Recurrence Interval 10-yr 50-yr 10O-vr 500-vr Upstream Study 715 2460 3295 6600 Limit Broadway 795 2685 3590 6900 19th Street 735 2660 3580 6900 28th Street 865 2565 3470 6800 SH 119 910 2395 3335 6800 Confluence 830 2435 3360 6800 Boulder Creek F "I C C k Location Recurrence Interval lO-yr 50-yr lOO-yr 500-yr Wonderland 90 190 250 860 Lake Outfall Broadway 205 415 530 1600 Between 15th 280 410 530 1700 and 19th St. 19th Street 280 560 720 2100 28th Street 405 820 1055 2300 4ih Street 565 1085 1400 2400 Confluence 605 1155 1480 2700 Goose Creek Wonderland Creek The impact of the spill from Fourmile Canyon Creek on the flood peaks of both Creeks was examined. The spill discharge along the south bank of Fourmile Canyon Creek was quantified using HEC-RAS. The analysis indicated significant spills occurred along FOllnnile Canyon Creek in the vicinity of Broadway Street during the 50-, 100- and 500- year events. The spill flows leave the Fourmile Canyon Creek Catchment and enter the Wonderland Creek Catchment traveling south and southeast. They enter Wonderland -9-